[esolyt]

There are two possible ways to interpret this:

1. "A Mac is susceptible to viruses. But it is not susceptible to viruses plaguing Windows-based computers."

2. "A Mac isn’t susceptible to viruses, whereas a Windows-based computer is susceptible to thousands of viruses."

The fact that you still get viruses, but they just don't happen to be the same viruses, isn't worth stating. So as a customer, it is very unlikely that I would infer the former (Meaning 1) from the statement. Yet it is what is meant.

I would personally call this misleading (and dangerously close to lying).